WO 02/13647 A2 discloses a process for producing a hook and loop fastener part, with a plurality of molded elements made symmetrically and connected integrally to a support web. Each molded element is in the form of interlocking means having a stalk with a head part. A moldable material is supplied to the shaping zone between a pressure tool and a molding tool. In the known process, viewed at least in a longitudinal section of a mold cavity, the opposing boundary walls extend continuously convexly. A continuously extending transition between the cross sectional shapes of the stalk and head part for an interlocking means of the support is achieved, so that an unimpeded mold removal process results.
In this process, a suitable plastic granulate is plasticized via an extruder, and is supplied to the extruder nozzle of the extruder for delivery to the molding tool. The plastic material used for this purpose generally leads to colorless hook and loop fastener parts of limited transparency. If the finished hook and loop fastener product is to be colored, the plastic granulate used can be already colored and supplied it to the product process (master batch), or color pigments, for example, in the form of titanium oxide, can be added to the plastic granulate, for coloring white and then supplied to the production process. Since the dyes used for this purpose, in addition to dye pigments, have chemical and mechanical behavior not exactly known to the custom molder and are dictated by the manufacturer, in the actual course of the production process problems may arise, especially with respect to removing the individual finished molded elements from the mold cavities of the molding tool.
When white dyes in the form of titanium dioxide color pigments are added, the melt flow index (MFI) measured in grams per 10 minutes for the plastic material has been found clearly to deteriorate. This coloring process cannot be used at all in master batch operation for micro-hook and loop fasteners. Because of the very poor flow behavior of the plastic, it can no longer be delivered into the exceptionally geometrically small cavities (mold cavities) of the molding tool. Attempts undertaken in practice to improve the molding behavior such that the molding temperature for the plasticized plastic material is increased, however generally lead to temperature ranges being reached which damage the plastic material and make production of hook and loop fastener products in that range of sizes impossible. It is also difficult, without major cleaning effort on the extruder, to switch from one color to the next for the finished hook and loop fastener product during the production process which proceeds more or less continuously.
To remedy this problem, the prior art (JP 07213310 A, JP 02283305 A and WO 00/73063 A1) has already suggested coloring or/or printing of male and/or female engagement parts of pressure sensitive adhesive fasteners by inkjet or electrostatic application processes. On the one hand, extensive freedom of shaping in color application in these processes is not possible. On the other hand, these processes can only be economically carried out when large amounts of fastener material to be produced are colored with a dye. These processes are in turn limited in their application, if micro-hook and loop fasteners are to be tinted in this way.
U.S. Pat. No. 6,136,046 discloses inkjet dye application processes, in addition to electrostatically acting systems and ultrasonic systems, also using piezoresistive element systems for dye application. These processes also have application limits if hook and loop fasteners are to be tinted with them, since the projecting head parts on the ends of the fastener stalks form undercuts with them. The undercuts can only be covered with difficulty by dye application from the outside. If, as is recognized, the color is also applied only to the top of the hook and loop fastener material, it fundamentally wears leading to decoloration of the fastener product over the long term. Conditions are comparable when the fastener material is printed with dye or the dye is doctored onto the fastener material. Stria formation often occurs unintentionally, as do problems in drying of the dye leading to loss of quality. To be able to ensure reliable adhesion of the dye at all, “priming” and/or additional surface treatment processes are necessary.